In the field of automotive engineering, for example, wiring systems are frequently used in the form of loose bunches of conductors which are not provided with an outer cable sheath. Such wiring systems can comprise a large number of conductors which have different dimensions and which must be installed in the vehicle. For simplifying such wiring systems and for arranging them in a clearer mode of arrangement, their conductors (lines), which may be routed over prolonged distances up to the connection point, are bundled so as to form a cable harness. Such a cable harness is normally formed by combining on a nail board, a plurality of conductors which have been cut to their respective required longitudinal dimensions and by binding said conductors together by cable belts or plastic bands, whereupon they are secured by means of clamps to the chassis or to another part of the vehicle.
If such a cable harness is guided through partition panels, e.g. from the engine compartment of a passenger car into the car interior, there is the risk that moisture, such as condensation water or splash, creeps along the surfaces of the conductors or on the surfaces of bunches of conductors and reaches bare electric wires at the conductor ends and enters e.g. into the attachment plugs of the electronic system of an engine where they may cause short circuits and, consequently, severe failures.
DE 36 31 769 Al discloses that, for forming a longitudinally water-tight section in a predetermined area of a multi-conductor wiring system, such as a cable harness, the spaces (interstices) between the individual conductors are filled with a plastic material in the predetermined area to be sealed, whereupon a shrinkable hose is pushed onto the outer circumference of the wiring system in the area of the section to be sealed and caused to shrink closely onto the circumference of said wiring system by the supply of heat. The filling of the spaces (interstices) between the individual conductors as well as between the inner surface of the shrinkable hose and the outer conductors of the wiring system is carried out by embedding an element of plastic material between the conductors before the shrinkable hose is pushed on; said element of plastic material swells up in the course of the heat treatment so that its cross-sectional shape is enlarged and it consists of or includes a thermoplastic hot-melt adhesive which, when heated, melts, foams and, in so doing, forms closed pores.
U.S. Pat. No. 4,997,689 to Langen, et al. ("Langen") discloses a "dual strip" method for sealing multiple-strand cable bundles in a longitudinally watertight manner. Langen is referred to as a "dual strip" method because it comprises a sealing strip having two adhesive components, a melt adhesive forming the bulk of the adhesive components and butyl rubber in a much less amount than the melt adhesive component. In addition to the two adhesive components, the sealing strip has a non-sticky release paper layer. The melt adhesive of Langen is a plastic material which after heating to about 130.degree. C. will melt, thereby forming a sticky melt. Thus, the melt adhesive is a polymer having a relatively high melting point which provides the required sealing effect as it penetrates in its molten state into voids existing between neighboring conductors and between conductors and a surrounding shrinkable hose. The Butyl rubber component does not play a role in the sealing effect as it is merely present in a much smaller amount than the melt adhesive and is mainly used to allow the temporary fixing of the cable strands in a side by side relation before the addition of heat. Thus, the Butyl rubber component is used as a positioning aid which keeps the cable strands in the side by side orientation during subsequent winding or folding and heating.
After winding or folding the cable strands and before the heating of the melt adhesive, an outer heat shrinkable hose is applied around the portion to be sealed. Thus, the application of heat not only melts the melt adhesive but effects the shrinking of the heat shrinkable hose, thus exerting a nominal compressive force onto the cable bundle.
While the method of Langen has its advantages, the high temperatures needed to melt the melt adhesive are apt to cause damage to the insulative sheaths provided around each of the conductors comprising the cable bundle. At temperatures of 130.degree. C., many plastic insulative sheathes are softened or melted thereby provoking the risk of unacceptable electric shorts within the cable bundle. Additionally, the outer shrinkable hose must be selected that can withstand the required high temperatures without damage and which can reliably shrink at the required high temperatures. Lastly, the pressure supplied by the outer shrinkable hose on the cable bundle is relatively weak, approximately 30N measured over a length of 30 mm. This weak compressive force is not enough to effectively force the melt adhesive into all voids existing between neighboring cable strands, nor will it effectively squeeze all voids and pores existing in the melt adhesive itself.
In fact, the methods of Langen have failed to meet the specification of European automobile manufacturers to provide 100% longitudinal water tightness within a conductor bundle for a useful life of at least 3000 hours at temperatures of 105.degree. C. (which may occur in the engine compartment of today's automobiles).
Persons skilled in the art also know that longitudinally water-tight sections in wiring systems, such as cable harnesses, can be produced by filling the spaces (interstices) with the aid of molten casting resins, by enveloping the conductors by means of injection molding, by kneading-in sealing compounds, or by embedding the conductors in a gel.
All these courses of action known in the prior art have the following disadvantages in common:
lack of reproducibility; PA1 long processing times; PA1 complicated handling; PA1 the risk that the electric conductors or other electric/electronic components may be thermally damaged because of the high temperatures required; PA1 high total-costs; and PA1 in some cases, substantial enlargement of the sealing point as well as the necessity of at least one additional phase of operation while mounting (e.g. a cable harness).